Create a new transparent drawing, 400 x 400.
Using Ellipse Select tool, create a circle about 100 x 100 pixels in the center of the drawing. Use the settings shown below:
Fill with a metallic gradient, I am using "Metallic Something" (that's the name) with the shape set to radial. Drag the cursor from the center point of the circle outward to the edge of the circle. It doesn't matter where you click out from center as long as it's on the edge of the circle.
Create a new transparent layer, using the same Ellipse Select tool settings as above, and create a new smaller circle over the top of the larger circle, and fill the circle with black, and then press delete to remove the black:
You'll notice that the layer below is showing. Switch to the lower layer and press delete again, creating your "donut hole".
Select-None or Shift+CTRL+A.
Merge the top layer down. DO NOT FLATTEN. You want to maintain the transparency.
Save the image as "metalspring.gih".
At the menu prompt that follows, use the following settings:
Save the file to your .gimp-2.6/brushes folder, refresh your brushes in the brush dialog, and go try out your new spring brush.
First example using as a gradient, second as original brush.
(Note: if you want the brush to have a more tubular look, simply open the Brushes Dialog and with the spring brush selected , change the spacing setting located at the bottom of the dialog box: see image below)
Example of same brush saved with spacing set to 1: